Embodiments of the invention relate generally to electrical circuitry, and, more particularly, to micro-electromechanical system (MEMS) based switching devices, and, even more particularly, to a system and method for avoiding a tendency of switch contacts to stick to one another without interrupting system operation.
A circuit breaker is an electrical device designed to protect electrical equipment from damage caused by faults in the circuit. Traditionally, most conventional circuit breakers include bulky electromechanical switches. Unfortunately, these conventional circuit breakers are large in size thereby necessitating use of a large force to activate the switching mechanism. Additionally, the switches of these circuit breakers generally operate at relatively slow speeds. Furthermore, these circuit breakers are disadvantageously complex to build and thus expensive to fabricate. In addition, when contacts of the switching mechanism in conventional circuit breakers are physically separated, an arc is typically formed there between which continues to carry current until the current in the circuit ceases. Moreover, energy associated with the arc may seriously damage the contacts and/or present a burn hazard to personnel.
As an alternative to slow electromechanical switches, it is known to use relatively fast solid-state switches in high speed switching applications. As will be appreciated, these solid-state switches switch between a conducting state and a non-conducting state through controlled application of a voltage or bias. For example, by reverse biasing a solid-state switch, the switch may be transitioned into a non-conducting state. However, since solid-state switches do not create a physical gap between contacts when they are switched into a non-conducting state, they experience leakage current. Furthermore, due to internal resistances, when solid-state switches operate in a conducting state, they experience a voltage drop. Both the voltage drop and leakage current contribute to the dissipation of excess power under normal operating circumstances, which may be detrimental to switch performance and life.
MEMS switching devices can offer notable advantages over traditional electromechanical switches and solid-state switches. It has been observed, however, that MEMS switching devices can exhibit contact stiction or a tendency of contacts of the switch to stick to one another (e.g., the switch contacts can remain closed when commanded to open, or can exhibit an unacceptable time delay in opening when commanded to open) after having been closed for a relatively long period of time, which may vary depending on the characteristics of a given switch.
It is known that contact stiction can occur, for example, due to metal diffusion over time of contact materials. This stiction phenomenon is likely to occur in operational situations when the switches are used in applications—such as circuit breaker applications—where the normal operating state of the switch is closed. This can lead to degraded performance when the switching device takes longer to open than a specified switching time, and can even lead to a failure when the switch fails to open at all. Accordingly, it is desirable to provide a system and/or control techniques for reducing or avoiding this tendency to stick of MEMS switching devices and thus incrementally contribute to the overall reliability of the system and/or application in which the switch is used.